During the processing of molten steel in a ladle, an inert gas such as argon is typically bubbled into and through the molten steel. The bubbling of inert gas into the ladle facilitates uniform composition, uniform temperature control, oxygen removal, and purification of molten metal in the ladle. One conventional method of injecting the inert gas into the ladle involves the use of a port in the floor of the ladle. The space defining the port is occupied by a porous plug. Inert gas (typically argon) is continuously passed into the ladle through the porous plug, whereby the porous plug a) divides the inert gas into small bubbles and b) prevents molten metal from seeping into the gas inlet port, as long as the gas is being injected.
Conventional porous plugs have typically been constructed from a ceramic porous brick material surrounded by a steel shell, and held into place by a refractory mortar. The typical porous plug includes a large number of irregular interconnected passages resembling the openings in a sponge. Porous plugs having regular interconnected passages are also known.
Conventional porous plug structures are not very durable and tend to erode quickly, requiring frequent replacement. The tendency to erode, and become blocked, is due in part to the high temperatures in the ladle, which can reach 2700.degree.-2900.degree. F. Therefore, there is a need or desire in the iron and steel industry for porous plugs useful in ladle ports which accomplish all the objectives of conventional porous plugs, yet which are more durable and have much longer useful lives.